The modern soldier is equipped with an ensemble of protective clothing. Part of the ensemble is ballistic protection which is typically comprised of a soft ballistic vest that provides fragmentation and hand gun protection. The ballistic vest has large plate pockets on the front and rear into which can be inserted hard armor plates that protect against high velocity ballistic threats. A recurring issue for ballistic protection ceramic body armor plates such as the SAPI (Small Arms Protective Insert) and ESAPI (Enhanced Small Arms Protective Insert) and other configurations of body armor with a ceramic strike face, is that it is very difficult to determine the integrity of the ceramic plate when they are in service. To obtain optimal ballistic protection and performance from a ceramic plate it is necessary that the ceramic strike face be free from cracks and fractures that would compromise the ability of the ceramic to defeat a ballistic threat when it is impacted.
When plates are in service and especially when in theatre they are subject to the rigours of the battlefield. The plates are very heavy with a weight that ranges between 2.5 and 4.5 kilograms each, depending on size and construction material, with usually two plates provided per vest. As a result of their weight, the plates are repeatedly banged and struck against hard objects. Even through such simple activities as when the vest is taken off and put down on the ground the ceramic may be damaged. The plates are constructed with a fabric or plastic cover over the entire plate and depending on the design may have thin layers of additional materials such as polycarbonate, plastics or foam on the ceramic strike face to afford it some protection from bumps. All these layers and covers make it impossible to determine the integrity of the ceramic and whether or not the plate should stay in service when the plate is inspected visually. Conventional means of Non Destructive Technology (NDT) that are used to inspect composite/ceramic structures include air coupled and immersion ultrasonics, Infrared and laser thermography, eddy current and digital x-ray require involved equipment and facilities or specialized technical skills. In addition several of these techniques cannot be used when a plate has any type of protective cover on it as the ceramic component needs to be directly accessed. As a body armor plate cannot be stripped of its protective cover to see if it may be damaged, the inspection method being promoted for in-field inspection and being implemented by the US Army is to inspect armor with portable digital x-ray systems. Even small digital x-ray testing capability however is not typically found in theatre and definitely not at forward operating bases where the hard armor is placed into daily active service to protect the soldiers. To accommodate the inspections that are made away from the forward battlefield, increased supplies of hard armor plates must be purchased to provide sufficient stock for rotation through inspection. A test method must therefore be implemented that can be used by the soldier, takes less than 5 seconds for a result indication, is not an inconvenience to the soldier, and is rugged and reliable.
Prior art does exist for determining ceramic plate integrity, however for a number of reasons it is difficult to apply the prior art devices in the battlefield.
Kelsey (U.S. Patent 2007/7,180,302) “Method and system for determining cracks and broken components in armor”, describes how a ceramic plate can be screened with conductive traces of various patterns. The conductive circuit must be accessed by a user at electrical contacts provided in the system. The circuit is arranged so that damage, such as cracks that occurs within the ceramic component, can propagate into the conductive material forming the circuit and thereby cause a rupture in the conductive circuit. A voltage source or electrical probe such as an ohmmeter is used to measure the conductive circuit resistance that is then checked against an expected resistive value. The results are used to determine if the ceramic armor component is in operable condition.
Kelsey et al describe an electrical connector that is preferably integrated into or at an edge of the armor system. The connector or contact pads must have an elastomeric seal or dust cover to protect the terminals to which a meter must be connected. There are several problems with the implementation within an in theatre environment. Firstly, physical connection must be made to the plate for it to be inspected. The proposed connector must therefore be designed such that it can withstand general use and abuse associated with the weight and impacts of an armor plate. The connector must be designed to be sufficiently robust such that it cannot be knocked off or damaged during insertion of the plate into a vest plate pocket. It must also withstand the repeated insertion of a connector or contact forces required by meter probes without separating the connector from the conductive ink traces on the plate which are very fragile.
Kelsey suggests known values of resistance are used to validate the integrity of the plate. In practice this is compromised by the screening of the conductive ink as the resistive value of the dried ink trace fluctuates depending on the thickness or width of trace and the quality of the electrical contact between the measuring equipment and the plates connector. Further there will always be meter wire and probe management issues within the battlefield environment.
Liu (US Patent Pending 2009/0043516 A1) “Method and Apparatus for Detecting Damage in Armor Structures” describes an inspection system that uses a minimum of four or more peizo-electric transducers that are bonded to either personal body armor or larger armor panels. Using a baseline scan response previously obtained, the plate is analysed to determine if it has structurally changed. The plate is interrogated with a laptop computer although a handheld device has been proposed. The system requires each transducer to be connected externally with cables, with the connection being made in any conventional manner. The system is therefore similar to Kelsey in that it requires external connection for a plate to be tested, albeit with a larger multi-pin connector. It is suggested that the storing of baseline information for individual body armor panels would not be a practical undertaking at a forward operating base making this technology very difficult to implement at the soldier user level. The system also has connector maintenance and interface issues for battlefield implementation as previously discussed with respect to Kelsey.